A suction pressure sensor is sometimes provided in an internal combustion engine to control the internal combustion engine. To detect intake air pressure by the suction pressure sensor, a pipe is disposed between the suction pressure sensor and an intake passage such as a surge tank, as described in Japanese Laid-Open Patent Publication 2000-88688 and Japanese Laid-Open Patent Publication 9-68066.
In such a pipe, water droplets generated in the surge tank may attach to a hole formed in the pipe. The water droplets may pass through the hole and enter a gas filter provided within the pipe or even enter the suction pressure sensor, preventing high-accuracy detection by the suction pressure sensor. In addition, the water droplets that enter the pipe may freeze in a cold region thereby causing the pipe, the gas filter, or the suction pressure sensor to break.
Japanese Laid-Open Patent Publication 2000-88688 discloses an annular thickened portion around a hole of a pipe to prevent water from entering the pipe by keeping water droplets that move along the wall surface of the surge tank away from the hole of the pipe.
In this document, only approach and intrusion of the water droplets that move along the wall surface of the surge tank into the pipe can be prevented but intrusion of water droplets that drift through intake air into the pipe via the hole cannot be prevented.
Japanese Laid-Open Patent Publication 9-68066 discloses an elongate cylinder extending around a hole of a pipe and another cylinder, wherein the structure of the dual cylinders prevents water from entering the pipe.
The structure of this document can stop water droplets that drift in through intake air. However, the inner cylinder of the dual cylinders is provided on the wall surface on which a hole of the pipe is provided while an outer cylinder is provided on the wall surface opposite to the pipe hole. This configuration makes the intake passage such as a surge tank complicated and locations to provide such a waterproof structure are limited, which extremely reduces the degree of freedom for location of the pipe.